The invention relates to a circuit arrangement for operating a semiconductor light source, comprising
connection terminals for connecting a power supply,
input filter means,
rectifier means,
a converter with a control circuit, and
output terminals for connecting the semiconductor light source.
The invention also relates to a signal light provided with such a circuit arrangement.
A circuit arrangement of the type mentioned in the opening paragraph is described in U.S. Pat. No. 5,661,645. Semiconductor light sources are being increasingly used as signal lights. In such an application, the advantages of a semiconductor light source over a customary incandescent lamp are a substantial improvement in service life and a substantial reduction in power consumption. Signal lights often form part of a complex signaling system, for example a traffic control system with traffic lights. In order to realize said advantages of semiconductor light sources on a large scale, it is necessary for the circuit arrangement to be retrofit with respect to the existing signaling systems.
In existing signaling systems, a signal light is often powered by means of a solid-state relay. A general property of solid-state relays is that a minimum current is required to bring the relay into the conducting state by means of a trigger current and to keep it in that state by means of a holding current. In existing installations, use is customarily made of an incandescent lamp having a load of 135 W. A semiconductor light source used as a signal light, however, customarily has a rated power in the range from 7 W to 20 W and a corresponding, lower current.
This constitutes a problem for the application of the circuit arrangement and the semiconductor light source provided with said circuit arrangement.
It is an object of the invention to provide a measure for completely or partly obviating said problem.
In accordance with the invention, this object is achieved in that the circuit arrangement of the type mentioned in the opening paragraph is characterized in accordance with the invention in that the part between the input terminals and the rectifier means is free of capacitive means. It has been found that this measure precludes in a surprisingly simple manner that, instead of being rendered conducting, the solid-state relay starts oscillating, which means that the solid-state relay switches with a high frequency between the conducting and the non-conducting state. Preferably, the input filter means are positioned between the rectifier means and the converter. This has the advantage that the construction of the circuit arrangement remains relatively simple, while it is precluded that the solid-state relay and the input filter means can jointly form an oscillating circuit. Surprisingly it has also been found that positioning the rectifier means between the input terminals and the input filter means results in more effective filtering by said filter means. This enables, on the one hand, a further reduction in interference to be achieved when unchanged use is made of the known input filter means, and, on the other hand, the use of simpler input filter means when an unchanged level of interference suppression is accepted.
In an advantageous embodiment of the circuit arrangement in accordance with the invention, the input filter means comprise a differential-mode filter. A very suitable differential-mode filter is a xcfx80 filter.
In this description and in the claims, the term converter is to be taken to mean an electric circuit by means of which an electric power supplied by the power supply is converted to a required current and voltage combination for operating the semiconductor light source. For this purpose, use is preferably made of a switch mode power supply provided with one or more semiconductor switches.
Preferably, a signal light provided with a housing accommodating a semiconductor light source in accordance with the invention is also provided with the circuit arrangement in accordance with the invention. In this manner, the possibilities of using the signal light as a retrofit for an existing signal light are substantially increased. If the circuit arrangement is provided with a housing which is integrated with the housing of the signal light, an optimum range of applications as a retrofit signal light is created.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.